Pressure sensors are used in a variety of areas, such as automotive and industrial applications, to provide an electrical signal corresponding with a measured fluid pressure. For example, pressure sensors can be used to measure automotive oil pressure and hydraulic fluid pressure.
One type of pressure sensor includes a solid state pressure sensing bridge, or chip, for generating an electrical signal corresponding with fluid pressure applied to the chip. Typically, the chip is mounted within a cavity of a base, and a fluid medium (e.g., silicone gel) is placed within the cavity to cover the chip. A diaphragm is secured to the base over the cavity to secure the gel within the cavity, and to create a sealed pressure sensor package. Alternatively, the gel can be injected into the cavity through a separate port after the diaphragm is secured to the base. In operation, pressure applied to the diaphragm deflects the diaphragm, is transmitted by the medium, thereby resulting in pressurization of the chip.
The diaphragm is commonly secured to the base by welding. Welding provides an adequate seal, but the operation can only be performed if both the base and the diaphragm are made of compatible metallic materials. In addition, the welding operation can be expensive, and can cause heat distortion of the components. Also, the welding typically must be done without the fluid medium in the cavity, thereby requiring the extra operations of injecting the fluid medium into the cavity and thereafter sealing the cavity without causing an unacceptable pressure offset pressure in the cavity.